This unit relates generally to apparatus and methods for manufacturing MEMS (micro-electromechanical systems) by forming a multiplicity of such devices on a silicon wafer. More specifically, the invention relates to a process for manufacturing a multiplicity of very flat (e.g. having a radius of curvature greater than 40 meters) two-axis silicon elliptical mirrors used for optical switching and other light beam steering applications by minimizing the microloading effect during plasma etching.
MEMS devices are becoming more and more available and common. However, these devices are extremely small compared to regular machines, but still very large when compared to the individual circuits or components and features found on IC""s and other electronic chips. Some MEMS devices such as the digital micromirror device arrays produced by Texas Instruments are made significantly smaller than most other types of MEMS devices, but are also very large compared to components on an IC or other chips and use existing geometry and patterning techniques common for the productions of semiconductor circuits. For example, small analog MEMS devices used for optical switching of transmitted data streams may have a size in the millimeter range, whereas the mirrors on micromirror arrays used for display devices are typically between about 15-20 microns on a side. Thus, it is seen that MEMS devices are not comfortably compared with either full-size machines or devices (they are much smaller) or a true array of micro devices such as IC""s, memory chips, and the like (they are much larger).
Known processes for fabricating MEMS type mirrors include micro-machining polysilicon, using SOI (silicon on insulator) wafers. Mirrors produced by this process however, are typically very thin and consequently maintaining the desired flatness is very difficult.
The present invention provides a process for manufacturing a plurality of MEMS devices on a first layer of material, such as for example, a thin wafer of silicon typically having a thickness of about 115 xcexcm. The process comprises attaching the thin silicon wafer to a carrier or backing wafer and then defining boundaries and features for each individual device of said plurality of devices with a constant line width.
After defining or placing the lines which define the features of the individual devices and the boundary or separation lines between individual devices, the wafer while attached to the backing wafer is etched such that both the separation lines and lines defining features on the device are etched through the selected thickness. The use of a constant line width helps eliminate over-etching or under-etching due to the phenomenon called microloading. Microloading is the differential etch rate between wide lines and narrow lines (wide lines etch faster) in a plasma reactor.
The devices are then separated from the backing layer. It should also be noted that the wafer used to manufacture the mirrors or the devices could be silicon or another suitable material. Further, the wafer may also undergo other processing steps before and after the etching process. For example, electronics, sensors or other mechanical features can be created by standard IC or MEMS fabrication processes before the etching step, and a reflective coating such as gold may be applied before the devices are separated from the backing layer.